1. Field of the Invention
The present invention relates to the field of symmetrical strip line type microwave circuits made with multilayer printed circuit techniques.
More particularly, an object of the present invention is an input-output connection zone for a circuit such as this.
2. Description of the Prior Art
The invention thus concerns a symmetrical strip line type microwave circuit, made by techniques employed in the multilayer printed circuit industry. In other words, this circuit, as shown in an exploded, sectional view in FIG. 1, comprises:
a first, insulating substrate 1, one face of which bears a conductive layer 4 forming a ground plane, while the other face bears a conductive pattern 3 forming the central conductor of the symmetrical strip line circuit;
a second, insulating substrate 2, with one of its faces designed to be placed on the central conductor 3; the other face of the substrate 2 bears a conductive deposit 5 forming a second ground plane.
It would thus seem that the central conductor 3 is sandwiched between the two insulating substrates 1 and 2.
To connect a circuit such as this to the components of the adjacent circuits, it is necessary to make a connection zone where the central conductor 3 will be accessible, that is, it will be necessary to expose the central conductor to the open.
To this effect, there is the following prior art procedure: the pattern designed to form the central conductor is deposited on the substrate 1, the other face of which is metallized. Before bonding the second substrate 2 to the first one, a scallop is made in the substrate 2. The geometry of this scallop is such that a portion of the central conductor 3 is exposed to the open and it is possible to fix a connection thereto. However, this method has drawbacks. For, it is necessary to have a protective film, generally of the varnish type, deposited by brush, on the zones thus designed to be exposed to the open, so that they are not damaged during the subsequent steps of the fabrication. At the end of fabrication, this varnish should, of course, be removed by means of solvents. This implies additional operations which should be performed with great precision and are, furthermore, difficult to automate and are, therefore, expensive.